Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
impallesco (inp-), lŭi, 3, v. inch. n. [in-pallesco], to grow or turn pale in or at any thing (post-Aug.): nocturnis chartis, Pers. 5, 62: eventu impalluit ipse secundo, Stat. Th. 6, 805.